Polystyrene foam slabs or forms are widely used for thermal and acoustic insulation in building construction. The conventional process for the production of a polystyrene foam slab or form is as follows:
1. Expandable polystyrene is supplied from the manufacturer in particulate form graded for particle size. This particulate polystyrene has a proportion of blowing agent such as pentane dissolved in it.
2. The particles are exposed to heat, usually by steam, in a fluidised bed. As the particles pass from the bottom of the fluidised bed to the top, they soften and as the pentane is lost from solid solution, the released gas causes the softened polystyrene particles to expand up to fifty times their original volume. The particles become approximately spherical with a very low density. The expanded polystyrene particles are collected at the top of the bed. The particles still contain a small amount of pentane after this primary expansion process.
3. The dry particles are introduced into moulds the walls of which are penetrated by many small apertures. The dry particles may then be compressed. Steam is introduced into the vessel containing the polystyrene particles. The polystyrene particles soften and the residual pentane is released. In this second stage the volume expansion of the charge is contained by the mould walls forcing the particles together and fusing them to form a single, lightweight mass of expanded polystyrene foam.
4. If the mould is in the form of a block, the blocks of expanded polystyrene are subsequently sliced into slabs. These slices may be used as the cores of insulating walls or panels.
A disadvantage of polystyrene foams is their high propensity to burn and/or melt in a fire leading to the loss of structural strength. In contrast, foams with a phenolic resin matrix, that is phenolic foams, as a class of materials, are known for their excellent fire resistance and thermal properties, but their commercial potential in many fields of application is impeded due to their poor structural properties characterised by high brittleness and friability.
It would be desirable to identify new foam products that address the above limitations and further desirable to employ manufacturing processes which utilise commonly employed process equipment such as steam block moulding.